In context of construction and completion of a subterranean well, stringent safety requirements are imposed on the responsible party. It is important to protect personnel, the surrounding environment and also drilling- and production equipment from the formations being intervened. High pressure- and temperature differences may challenge the work carried out in the well. Well barriers are loops having one or more cooperating well barrier elements which prevent fluids from flowing in an undesirable manner from the formation, either into another formation or up to surface. In accordance with NORSOK standard D-010 (Well integrity in drilling and well operations), one barrier loop is required in a well exposed to dangers of uncontrolled cross flows between the formation zones in the well, whereas two barrier loops are required in a well exposed to dangers of uncontrolled blowouts from the well and into the environment. Intact barrier loops are prerequisites for allowing the work to be carried out in accordance with the standard, and at no or minimum risk of undesireable events taking place. Various forms of plugs, oftentimes made of cement, may be important well barrier elements both in primary and secondary barrier loops. In accordance with the standard, at least 100 meters of cement or another suitable plugging material is required, among other things, to be present from the casing shoe, which is located at a lower portion of a casing, and upwards within the annulus around the casing. It is known for the integrity of the annulus plug to become damaged due to weak formations, or due to impurities in the annulus preventing good circulation and adhesion of the plugging material, and also due to poor quality of the very plugging material, among other things, whereby the plugging material does not satisfy the sealing requirement after some time. Typically, substantial pressure increases in the various annuli in the well will be indications of a “poor cement job”. Both old and new wells may have to be drilled out again to evade the problems of poor or difficult barrier plugs, which will incur substantial additional costs to an operator.